Re: [Bluez PATCH v1] a2dp: Fix crash in channel_free while waiting cmd resp

From: Yun-Hao Chung <redacted>

When channel_free is called and we are waiting for a command response
from the peer, bluez NULL the setup->session but would not free its
setup_cb. Since setup_cb holds a ref of setup, the setup wouldn't be
freed and if service_removed is called after channel_free, a2dp_cancel
tries to abort the ongoing avdtp commands, which accesses the
setup->session and triggers a crash.

This change finalizes all avdtp commands before assigning setup->session
to NULL in channel_free.

Crash stack trace:
0x000059f01943e688      (bluetoothd -avdtp.c:3690)
avdtp_abort
0x000059f01943928a      (bluetoothd -a2dp.c:3069)
a2dp_cancel
0x000059f0194377fa      (bluetoothd -sink.c:324)
sink_unregister
0x000059f01948715a      (bluetoothd -service.c:177)
service_remove
0x000059f01948d77c      (bluetoothd -device.c:5346)
device_remove
0x000059f019476d14      (bluetoothd -adapter.c:7202)
adapter_remove
0x000059f019476c3e      (bluetoothd -adapter.c:10827)
adapter_cleanup
0x000059f01949d8d7      (bluetoothd -main.c:1114)               main
0x0000787b36185d74      (libc.so.6 -libc-start.c:308)
__libc_start_main
0x000059f019433e39      (bluetoothd + 0x00026e39)               _start
0x00007fff2d2c0127

Reviewed-by: Archie Pusaka <redacted>
---
There are two other options to fix this crash.
1. add a NULL check in a2dp_cancel before calling avdtp_abort.
2. call setup_cb_free to every setup_cb in setup->cb in channel_free.

Since each setup_cb needs setup->session, I think there is no need to
keep the setup_cb after assigning setup->session to NULL. So the first
option is not ideal. If the second option is adopted, there would be
some time that sink/source->connect_id/disconnect_id is not zero, but
there is no corresponding setup_cb.

Test steps:
Reproduce the crash with the following steps. Verify the crash is
no longer observed after this change.
1. ignore AVDTP_SET_CONFIGURATION resp by modifying avdtp.c
2. turn on a paired headset
3. check the bluetooth.log, while bluez is waiting for
   AVDTP_SET_CONFIGURATION resp, stop bluetoothd immediately.
   This will trigger:
   session_cb (I/O error) -> connection_lost
   -> avdtp_set_state (AVDTP_SESSION_STATE_DISCONNECTED)
   -> avdtp_state_cb -> channel_remove -> channel_free
   then:
   adapter_cleanup -> adapter_remove -> device_remove -> service_remove
   -> a2dp_sink_remove -> sink_unregister -> sink_free -> a2dp_cancel
4. check if bluetoothd crash
The above steps can trigger the crash 100%.

 profiles/audio/a2dp.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/profiles/audio/a2dp.c b/profiles/audio/a2dp.c
index d31ed845cbe7..f201b98c79d0 100644
--- a/profiles/audio/a2dp.c
+++ b/profiles/audio/a2dp.c

@@ -1540,9 +1540,14 @@ static void channel_free(void *data)
        setup = find_setup_by_session(chan->session);
        if (setup) {
                setup->chan = NULL;
+               /* Finalize pending commands before we NULL setup->session */
+               finalize_setup_errno(setup, -ENOTCONN, finalize_discover,
+                                                       finalize_select,
+                                                       finalize_config,
+                                                       finalize_resume,
+                                                       finalize_suspend, NULL);